The regulation of the CNS innate immune response is vital for the restoration of tissue homeostasis (repair) after acute brain injury: a brief review

First study on response of astrocytes in alevines of red-bellied pacu (Piaractus brachypomus) to subchronic exposure to chlorpyrifos and trichlorfon

Background and Aim: Organophosphate pesticides (OPs) used in agricultural production pose environmental and public health risks whenever non-target organisms are exposed to them. Oxon-type OPs, such as trichlorfon (TCF) and chlorpyrifos (CPF), are frequently used in Colombia and have been detected in water bodies in the vicinity of croplands; however, their effect on aquatic organisms, especially fish, is largely unknown. The neurotoxicity of OPs includes inhibition of esterase enzymes, neuronal damage, and increased glial reactivity. This study aimed to assess the astrocytic response in the brain tissue of juvenile red-bellied pacu (Piaractus brachypomus) exposed to TCF and CPF. Materials and Methods: A 25-day subchronic assay was conducted in which juvenile red-bellied pacu were exposed to CPF and TCF. After 25 days of exposure, the fish were killed and brain samples were collected and processed for immunohistochemistry to assess the morphology and reactivity of astrocytes; glial acidic fibrillary protein was used as a biomarker. Results: The brain samples from animals under subchronic exposure to OPs for 25 days showed higher cellular density as well as changes in astrocyte phenotype characterized by shortening of cytoplasmic projections, hypertrophy, and ameboid morphology compared to those from nonexposed animals. Similarly, astrocyte hyperreactivity was detected in the optic tectum and medial longitudinal fasciculus of the exposed group. Conclusion: Immunoreactivity of brain glial cells under subchronic exposure to OPs measured through immunohistochemical tests as well as OPs-induced neuropathology may be useful as a biomarker for monitoring environmental pollution. The results also indicate that P. brachypomus is a suitable biomonitoring model for studying neurotoxicological and neurodegenerative diseases.

Intertwined pathways of complement activation command the pathogenesis of lupus nephritis

The complement system is involved in the origin of autoimmunity and systemic lupus erythematosus. Both genetic deficiency of complement components and excessive activation are involved in primary and secondary renal diseases, including lupus nephritis. Among the pathways, the classical pathway has long been accepted as the main pathway of complement activation in systemic lupus erythematosus. However, more recent studies have shown the contribution of factors B and D which implies the involvement of the alternative pathway. While there is evidence on the role of the lectin pathway in systemic lupus erythematosus, it is yet to be demonstrated whether this pathway is protective or harmful in lupus nephritis. Complement is being explored for the development of disease biomarkers and therapeutic targeting. In the current review we discuss the involvement of complement in lupus nephritis.

NLRP1 Inflammasomes: A Potential Target for the Treatment of Several Types of Brain Injury

NOD-like receptor (NLR) family pyrin domain-containing 1 (NLRP1) is a member of the NLR family. The NLRP1 inflammasome consists of the NLRP1 protein, the adaptor protein apoptosis-associated speck-like protein containing a CARD domain, and the effector molecule pro-caspase-1. When stimulated, the inflammasome initiates the cleavage of pro-caspase-1 and converts it into its active form, caspase-1; then, caspase-1 facilitates the cleavage of the proinflammatory cytokines interleukin-1β and interleukin-18 into their active and secreted forms. In addition, caspase-1 also mediates the cleavage of gasdermin D, which leads to pyroptosis, an inflammatory form of cell death. Pathological events that damage the brain and result in neuropathological conditions can generally be described as brain injury. Neuroinflammation, especially that driven by NLRP1, plays a considerable role in the pathophysiology of brain injury, such as early brain injury (EBI) of subarachnoid hemorrhage, ischemic brain injury during stroke, and traumatic brain injury (TBI). In this article, a thorough overview of NLRP1 is presented, including its structure, mechanism of activation, and role in neuroinflammation. We also present recent studies on NLRP1 as a target for the treatment of EBI, ischemic brain injury, TBI, and other types of brain injury, thus highlighting the perspective of NLRP1 as an effective mediator of catastrophic brain injury.

Innate Immune Pathways Promote Oligodendrocyte Progenitor Cell Recruitment to the Injury Site in Adult Zebrafish Brain

The oligodendrocyte progenitors (OPCs) are at the front of the glial reaction to the traumatic brain injury. However, regulatory pathways steering the OPC reaction as well as the role of reactive OPCs remain largely unknown. Here, we compared a long-lasting, exacerbated reaction of OPCs to the adult zebrafish brain injury with a timely restricted OPC activation to identify the specific molecular mechanisms regulating OPC reactivity and their contribution to regeneration. We demonstrated that the influx of the cerebrospinal fluid into the brain parenchyma after injury simultaneously activates the toll-like receptor 2 (Tlr2) and the chemokine receptor 3 (Cxcr3) innate immunity pathways, leading to increased OPC proliferation and thereby exacerbated glial reactivity. These pathways were critical for long-lasting OPC accumulation even after the ablation of microglia and infiltrating monocytes. Importantly, interference with the Tlr1/2 and Cxcr3 pathways after injury alleviated reactive gliosis, increased new neuron recruitment, and improved tissue restoration.

Role of Vitamin E and the Orexin System in Neuroprotection

Microglia are the first line of defense at the level of the central nervous system (CNS). Phenotypic change in microglia can be regulated by various factors, including the orexin system. Neuroinflammation is an inflammatory process mediated by cytokines, by the lack of interaction between neurotransmitters and their specific receptors, caused by systemic tissue damage or, more often, associated with direct damage to the CNS. Chronic activation of microglia could lead to long-term neurodegenerative diseases. This review aims to explore how tocopherol (vitamin E) and the orexin system may play a role in the prevention and treatment of microglia inflammation and, consequently, in neurodegenerative diseases thanks to its antioxidant properties. The results of animal and in vitro studies provide evidence to support the use of tocopherol for a reduction in microglia inflammation as well as a greater activation of the orexinergic system. Although there is much in vivo and in vitro evidence of vitamin E antioxidant and protective abilities, there are still conflicting results for its use as a treatment for neurodegenerative diseases that speculate that vitamin E, under certain conditions or genetic predispositions, can be pro-oxidant and harmful.

COVID-Pain: Acute and Late-Onset Painful Clinical Manifestations in COVID-19 - Molecular Mechanisms and Research Perspectives

Although the respiratory manifestations of COVID-19 are predominant, signs and symptoms of an extra-pulmonary involvement are usually encompassed among the clinical picture of the disease. Several painful manifestations can occur during the acute phase but also as short- or long-term complications. Myalgia, joint pain, sore throat, abdominal pain, chest pain, and headache usually accompany respiratory symptoms, but they can also occur as isolated clinical findings or can be expressed regardless of the severity of COVID-19. On these premises, given the vast spectrum of clinical manifestations and the complexity of their pathogenesis, it would be more appropriate to refer to "COVID-pain", an umbrella term useful for encompassing all these clinical manifestations in a separate chapter of the disease. In this scenario, we addressed the topic from a molecular perspective, trying to provide explanations for the underlying pathophysiological processes. Consequently, this narrative review is aimed at dissecting the mechanisms of acute and chronic painful manifestations, summarizing fundamental concepts on the matter, controversies, current research gaps, and potential developments in this field.

Critical Roles of Lysophospholipid Receptors in Activation of Neuroglia and Their Neuroinflammatory Responses

Activation of microglia and/or astrocytes often releases proinflammatory molecules as critical pathogenic mediators that can promote neuroinflammation and secondary brain damages in diverse diseases of the central nervous system (CNS). Therefore, controlling the activation of glial cells and their neuroinflammatory responses has been considered as a potential therapeutic strategy for treating neuroinflammatory diseases. Recently, receptor-mediated lysophospholipid signaling, sphingosine 1-phosphate (S1P) receptor- and lysophosphatidic acid (LPA) receptor-mediated signaling in particular, has drawn scientific interest because of its critical roles in pathogenies of diverse neurological diseases such as neuropathic pain, systemic sclerosis, spinal cord injury, multiple sclerosis, cerebral ischemia, traumatic brain injury, hypoxia, hydrocephalus, and neuropsychiatric disorders. Activation of microglia and/or astrocytes is a common pathogenic event shared by most of these CNS disorders, indicating that lysophospholipid receptors could influence glial activation. In fact, many studies have reported that several S1P and LPA receptors can influence glial activation during the pathogenesis of cerebral ischemia and multiple sclerosis. This review aims to provide a comprehensive framework about the roles of S1P and LPA receptors in the activation of microglia and/or astrocytes and their neuroinflammatory responses in CNS diseases.

CD47 in the Brain and Neurodegeneration: An Update on the Role in Neuroinflammatory Pathways

CD47 is a receptor belonging to the immunoglobulin (Ig) superfamily and broadly expressed on cell membranes. Through interactions with ligands such as SIRPα, TSP-1, integrins, and SH2-domain bearing protein tyrosine phosphatase substrate-1 (SHPS-1), CD47 regulates numerous functions like cell adhesion, proliferation, apoptosis, migration, homeostasis, and the immune system. In this aspect, previous research has shown that CD47 modulates phagocytosis via macrophages, the transmigration of neutrophils, and the activation of T-cells, dendritic cells, and B-cells. Moreover, several studies have reported the increased expression of the CD47 receptor in a variety of diseases, including acute lymphoblastic leukemia (ALL), chronic myeloid leukemia, non-Hodgkin’s lymphoma (NHL), multiple myeloma (MM), bladder cancer, acute myeloid leukemia (AML), Gaucher disease, Multiple Sclerosis and stroke among others. The ubiquitous expression of the CD47 cell receptor on most resident cells of the CNS has previously been established through different methodologies. However, there is little information concerning its precise functions in the development of different neurodegenerative pathologies in the CNS. Consequently, further research pertaining to the specific functions and roles of CD47 and SIRP is required prior to its exploitation as a druggable approach for the targeting of various neurodegenerative diseases that affect the human population. The present review attempts to summarize the role of both CD47 and SIRP and their therapeutic potential in neurodegenerative disorders.

The Role of Neuronal NLRP1 Inflammasome in Alzheimer's Disease: Bringing Neurons into the Neuroinflammation Game

The innate immune system and inflammatory response in the brain have critical impacts on the pathogenesis of many neurodegenerative diseases including Alzheimer's disease (AD). In the central nervous system (CNS), the innate immune response is primarily mediated by microglia. However, non-glial cells such as neurons could also partake in inflammatory response independently through inflammasome signalling. The NLR family pyrin domain-containing 1 (NLRP1) inflammasome in the CNS is primarily expressed by pyramidal neurons and oligodendrocytes. NLRP1 is activated in response to amyloid-β (Aβ) aggregates, and its activation subsequently cleaves caspase-1 into its active subunits. The activated caspase-1 proteolytically processes interleukin-1β (IL-1β) and interleukin-18 (IL-18) into maturation whilst co-ordinately triggers caspase-6 which is responsible for apoptosis and axonal degeneration. In addition, caspase-1 activation induces pyroptosis, an inflammatory form of programmed cell death. Studies in murine AD models indicate that the Nlrp1 inflammasome is indeed upregulated in AD and neuronal death is observed leading to cognitive decline. However, the mechanism of NLRP1 inflammasome activation in AD is particularly elusive, given its structural and functional complexities. In this review, we examine the implications of the human NLRP1 inflammasome and its signalling pathways in driving neuroinflammation in AD.

Complement and coagulation cascades in trauma

Trauma remains a major cause of death throughout the world, especially for patients younger than 45 years. Due to rapid advances in clinical management, both in the acute and prehospital settings, trauma patients survive devastating injuries at unprecedented rates. However, these patients can often face life threatening complications that stem from the robust innate immune response induced by severe hemorrhage, leading to further tissue injury rather than repair. The complement and coagulation cascades are key mediators in this disordered reaction, which includes the development of trauma‐induced coagulopathy. There is increasing evidence that cross‐talk between these two pathways allows rapid amplification of their otherwise targeted responses and contributes to overwhelming and prolonged systemic inflammation. In this article, we summarize the initial steps of innate immune response to trauma and review the complex complement and coagulation cascades, as well as how they interact with each other. Despite progress in understanding these cascades, effective therapeutic targets have yet to be found and further research is needed both to improve survival rates as well as decrease associated morbidity.

Piperlongumine Improves Lipopolysaccharide-Induced Amyloidogenesis by Suppressing NF-KappaB Pathway

Amyloidogenesis is known to cause Alzheimer's disease. Our previous studies have found that lipopolysaccharide (LPS) causes neuroinflammation and amyloidogenesis through activation of nuclear factor kappaB (NF-κB). Piperlongumine (PL) is an alkaloid amide found naturally in long pepper (Piper longum) isolates; it was reported to have inhibitory effects on NF-κB activity. We therefore investigated whether PL exhibits anti-inflammatory and anti-amyloidogenic effects by inhibiting NF-κB. A murine model of LPS-induced memory impairment was made via the intraperitoneal (i.p.) injection of LPS (0.25 mg/kg/day, i.p.). We then injected PL (1.5 or 3.0 mg/kg/day, i.p.) for 7 days in three groups of mice to observe effects on memory. We also conducted an in vitro study with astrocytes and microglial BV-2 cells, which were treated with LPS (1 µg/mL) or PL (0.5 or 1.0 or 2.5 µM). Results from our behavioral tests showed that PL inhibited LPS-induced memory. PL also prevented LPS-induced beta-amyloid (Aβ) accumulation and inhibited the activities of β- and γ-secretases. The expression of inflammatory proteins also was decreased in PL-treated mice, cultured BV-2, and primary astrocyte cells. These effects were associated with the inhibition of NF-κB activity. A docking model analysis and pull-down assay showed that PL binds to p50. Taken together, our findings suggest that PL diminishes LPS-induced amyloidogenesis and neuroinflammation by inhibiting NF-κB signaling; PL therefore demonstrates potential for the treatment of Alzheimer's disease.

The Neuro-Immune-Regulators (NIREGs) Promote Tissue Resilience; a Vital Component of the Host's Defense Strategy against Neuroinflammation

An effective protective inflammatory response in the brain is crucial for the clearance of pathogens (e.g. microbes, amyloid fibrils, prion^SC) and should be closely regulated. However, the CNS seems to have limited tissue resilience to withstand the detrimental effects of uncontrolled inflammation compromising functional recovery and tissue repair. Newly described neuro-immune-regulators (NIREGs) are functionally related proteins regulating the severity and duration of the host inflammatory response. NIREGs such as CD200, CD47 and CX3CL1 are vital for increasing tissue resilience and are constitutively expressed by neurons. The interaction with co-receptors (CD200R, CD172a, CX3CR1) will maintain microglia in the resting phenotype, directing aggressive microglia phenotype and limiting bystander injuries. Neurons can also express many of the complement NIREGs (CD55, CD46, CD59 and factor H). Neurons and glia also express suppressor of cytokine signaling proteins (SOCS) down regulating janus kinase-signal transducer and activator of transcription (JAK/STAT) pathway and to lead to the polarization of microglia towards anti-inflammatory phenotype. Other NIREGs such as serine protease inhibitors (serpins) and thrombomodulin (CD141) inhibit neurotoxic systemic coagulation proteins such as thrombin. The unfolded protein response (UPR) detects misfolded proteins and other stressors to prevent irreversible cell injury. Microglial pattern recognition receptors (PRR) (TREM-2, CR3, FcγR) are important to clear apoptotic cells and cellular debris but in non-phlogystic manner through inhibitory signaling pathways. The TYRO3, Axl, Mer (TAM) tyrosine receptor kinases activated by Gas 6 and PROS1 regulate inflammation by inhibiting Toll like receptors (TLR) /JAK-STAT activation and contribute to NIREG's functions.

Functional connectivity structure of cortical calcium dynamics in anesthetized and awake mice

The interplay between hemodynamic-based markers of cortical activity (e.g. fMRI and optical intrinsic signal imaging), which are an indirect and relatively slow report of neural activity, and underlying synaptic electrical and metabolic activity through neurovascular coupling is a topic of ongoing research and debate. As application of resting state functional connectivity measures is extended further into topics such as brain development, aging and disease, the importance of understanding the fundamental physiological basis for functional connectivity will grow. Here we extend functional connectivity analysis from hemodynamic- to calcium-based imaging. Transgenic mice (n = 7) expressing a fluorescent calcium indicator (GCaMP6) driven by the Thy1 promoter in glutamatergic neurons were imaged transcranially in both anesthetized (using ketamine/xylazine) and awake states. Sequential LED illumination (λ = 454, 523, 595, 640nm) enabled concurrent imaging of both GCaMP6 fluorescence emission (corrected for hemoglobin absorption) and hemodynamics. Functional connectivity network maps were constructed for infraslow (0.009–0.08Hz), intermediate (0.08–0.4Hz), and high (0.4–4.0Hz) frequency bands. At infraslow and intermediate frequencies, commonly used in BOLD fMRI and fcOIS studies of functional connectivity and implicated in neurovascular coupling mechanisms, GCaMP6 and HbO₂ functional connectivity structures were in high agreement, both qualitatively and also quantitatively through a measure of spatial similarity. The spontaneous dynamics of both contrasts had the highest correlation when the GCaMP6 signal was delayed with a ~0.6–1.5s temporal offset. Within the higher-frequency delta band, sensitive to slow wave sleep oscillations in non-REM sleep and anesthesia, we evaluate the speed with which the connectivity analysis stabilized and found that the functional connectivity maps captured putative network structure within time window lengths as short as 30 seconds. Homotopic GCaMP6 functional connectivity maps at 0.4–4.0Hz in the anesthetized states show a striking correlated and anti-correlated structure along the anterior to posterior axis. This structure is potentially explained in part by observed propagation of delta-band activity from frontal somatomotor regions to visuoparietal areas. During awake imaging, this spatio-temporal quality is altered, and a more complex and detailed functional connectivity structure is observed. The combined calcium/hemoglobin imaging technique described here will enable the dissociation of changes in ionic and hemodynamic functional structure and neurovascular coupling and provide a framework for subsequent studies of neurological disease such as stroke.

Ionizing Radiation-Induced Immune and Inflammatory Reactions in the Brain

Radiation-induced late brain injury consisting of vascular abnormalities, demyelination, white matter necrosis, and cognitive impairment has been described in patients subjected to cranial radiotherapy for brain tumors. Accumulating evidence suggests that various degrees of cognitive deficit can develop after much lower doses of ionizing radiation, as well. The pathophysiological mechanisms underlying these alterations are not elucidated so far. A permanent deficit in neurogenesis, chronic microvascular alterations, and blood–brain barrier dysfunctionality are considered among the main causative factors. Chronic neuroinflammation and altered immune reactions in the brain, which are inherent complications of brain irradiation, have also been directly implicated in the development of cognitive decline after radiation. This review aims to give a comprehensive overview on radiation-induced immune alterations and inflammatory reactions in the brain and summarizes how these processes can influence cognitive performance. The available data on the risk of low-dose radiation exposure in the development of cognitive impairment and the underlying mechanisms are also discussed.

CD200 restrains macrophage attack on oligodendrocyte precursors via toll-like receptor 4 downregulation

There are numerous barriers to white matter repair after central nervous system injury and the underlying mechanisms remain to be fully understood. In this study, we propose the hypothesis that inflammatory macrophages in damaged white matter attack oligodendrocyte precursor cells via toll-like receptor 4 signaling thus interfering with this endogenous progenitor recovery mechanism. Primary cell culture experiments demonstrate that peritoneal macrophages can attack and digest oligodendrocyte precursor cells via toll-like receptor 4 signaling, and this phagocytosis of oligodendrocyte precursor cells can be inhibited by using CD200-Fc to downregulate toll-like receptor 4. In an in vivo model of white matter ischemia induced by endothelin-1, treatment with CD200-Fc suppressed toll-like receptor 4 expression in peripherally circulating macrophages, thus restraining macrophage phagocytosis of oligodendrocyte precursor cells and leading to improved myelination. Taken together, these findings suggest that deleterious macrophage effects may occur after white matter ischemia, whereby macrophages attack oligodendrocyte precursor cells and interfere with endogenous recovery responses. Targeting this pathway with CD200 may offer a novel therapeutic approach to amplify endogenous oligodendrocyte precursor cell-mediated repair of white matter damage in mammalian brain.

Innate immune receptor Toll-like receptor 4 signalling in neuropsychiatric diseases

The innate immunity is a stereotyped first line of defense against pathogens and unspecified damage signals. One of main actors of innate immunity are the Toll-like receptors (TLRs), and one of the better characterized members of this family is TLR-4, that it is mainly activated by Gram-negative bacteria lipopolysaccharide. In brain, TLR-4 organizes innate immune responses against infections or cellular damage, but also possesses other physiological functions. In the last years, some evidences suggest a role of TLR-4 in stress and stress-related neuropsychiatric diseases. Peripheral and brain TLR-4 activation triggers sickness behavior, and its expression is a risk factor of depression. Some elements of the TLR-4 signaling pathway are up-regulated in peripheral samples and brain post-mortem tissue from depressed and suicidal patients. The "leaky gut" hypothesis of neuropsychiatric diseases is based on the existence of an increase of the intestinal permeability which results in bacterial translocation able to activate TLR-4. Enhanced peripheral TLR-4 expression/activity has been described in subjects diagnosed with schizophrenia, bipolar disorder and in autistic children. A role for TLR-4 in drugs abuse has been also proposed. The therapeutic potential of pharmacological/genetic modulation of TLRs signaling pathways in neuropsychiatry is promising, but a great preclinical/clinical scientific effort is still needed.

Signaling pathways regulating neuron-glia interaction and their implications in Alzheimer's disease

Astrocytes are the most abundant cells in the central nervous system. They play critical roles in neuronal homeostasis through their physical properties and neuron-glia signaling pathways. Astrocytes become reactive in response to neuronal injury and this process, referred to as reactive astrogliosis, is a common feature accompanying neurodegenerative conditions, particularly Alzheimer's disease. Reactive astrogliosis represents a continuum of pathobiological processes and is associated with morphological, functional, and gene expression changes of varying degrees. There has been a substantial growth of knowledge regarding the signaling pathways regulating glial biology and pathophysiology in recent years. Here, we attempt to provide an unbiased review of some of the well-known players, namely calcium, proteoglycan, transforming growth factor β, NFκB, and complement, in mediating neuron-glia interaction under physiological conditions as well as in Alzheimer's disease. This review discusses the role of astrocytic NFκB and calcium as well as astroglial secreted factors, including proteoglycans, TGFβ, and complement in mediating neuronal function and AD pathogenesis through direct interaction with neurons and through cooperation with microglia.

CD200 increases alternatively activated macrophages through cAMP-response element binding protein - C/EBP-beta signaling

The concept of macrophage polarization toward different phenotypes after CNS injury has been increasingly discussed. Here, we propose that CD200 treatment may help shift pro-inflammatory macrophages to an arginase 1 (Arg1)-, transglutaminase 2 (TGM2)-, and transforming growth factor beta 1 (TGF-β)-positive phenotype. Rat macrophages were stimulated by interferon γ and lipopolysaccharide (LPS) to induce pro-inflammatory phenotypes. Treatment with human CD200-Fc up-regulated expression levels of alternatively activated M2-like markers such as Arg1 and TGM2 but suppressed pro-inflammatory M1-like markers such as toll-like receptor 4, interleukin 1 beta (IL-1β), IL-6, and GM-CSF. Concomitantly, CD200-Fc enhanced (CCAAT/enhancer-binding protein) C/EBP-beta promoter activity, whereas NF-κB activity was suppressed. Treatment with CD200-Fc also up-regulated potentially beneficial TGF-β expression in macrophages. When C/EBP-beta signaling was suppressed with siRNA, the effect of CD200-Fc on Arg1, TGM2 and TGF-β up-regulation was canceled. Taken together, these data provide proof-of-principle that targeting CD200 signaling may be a novel therapeutic approach to shift macrophages toward M2-like polarization via modulating cAMP-response element binding protein-C/EBP-beta transcriptional activity. We showed that CD200 treatment decreased pro-inflammatory cytokines (IL-1β, IL-6, and GM-CSF) along with suppressed inflammatory NF-κB activity in pro-inflammatory Mφ. On the other hand, CD200 increased Arg1, TGM2, and TGF-β production through CREB-C/EBPβ signaling. We think that these findings provide proof-of-concept that CD200 signaling may play a key role in regulating macrophage polarization toward anti-inflammatory phenotypes.

Differential Effects of C1qa Ablation on Glaucomatous Damage in Two Sexes in DBA/2NNia Mice

PURPOSE

To determine the sex and age-related effects of C1qa ablation on retinal ganglion cell (RGC) and optic nerve (ON) axonal loss in a mouse model of glaucomatous neurodegeneration.

METHODS

Congenic C1qa mice were generated in the DBA/2NNia background. Female and male knockout (-/-), heterozygous (+/-), and wild type (+/+) mice were aged up to 14 months and IOPs were recorded in a subset of animals. Retinas of mice from all three groups at 5-6, 9-10 and 11-13 months of age were flat-mounted after retrograde labeling with Fluorogold. Imaged retinas were scored (RGC score) semi-quantitatively on a 10 point scale by two independent observers. A subset of retinas and optic nerves were also used for measurement of total number of RGCs. Semi-thin sections of ON were imaged and graded (ON score) for the amount of axonal damage semi-quantitatively, by two masked observers. Analysis of covariance (ANCOVA) was used for statistical comparisons. Microglial cells in flat-mounted retinas of 5-6 month old C1qa -/- and C1qa +/+ mice were used for assessment of microglial activation utilizing morphological criteria.

RESULTS

Female C1qa -/- mice had significantly higher IOP (p<0.000001, ANOVA) between 8 and 13 months of age compared to C1qa +/+ animals. No differences in IOPs between animals of the three genotypes were observed in males. At 5-6 months of age, there was no difference in RGC or ON scores between the three genotypes in animals of either sex. At 9-10 months of age, female mice didn't show significant differences in RGC or ON scores between the three genotypes. However, male C1qa -/- and C1qa +/- mice of the same age had better RGC and ON scores (p<0.003 and p<0.05, ANCOVA, for RGC and ON scores, respectively) compared with C1qa +/+ mice. At 11-13 months of age, female C1qa -/- mice had better RGC scores (p<0.006, ANCOVA) compared to C1qa +/+ and C1qa +/- animals. Accordingly, C1qa -/- mice had higher RGC counts (p<0.03, t-test) compared to C1qa +/+ animals. In male mice, there was a tendency for 12 month old C1qa -/- animals to have better RGC scores and higher RGC counts, but this didn't reach statistical significance. ON scores in 11-13 month old animals of either sex were not different between all three genotype. Microglial activation in male 5-6 month old C1qa -/- mice was decreased compared to C1qa +/+ animals; no such effect was seen in females.

CONCLUSIONS

Absence of C1qa ameliorates RGC and ON loss in the DBA/2NNia strain, but this effect differs between the two sexes. C1q-mediated RGC damage seems to be more potent than IOP-mediated RGC loss. In contrast, C1qa absence provides axonal protection early on, but this protection cannot overcome the effects of significant IOP elevation.

The immunomodulatory oligodendrocyte

Oligodendrocytes, the myelinating glial cells of the central nervous system (CNS), are due to their high specialization and metabolic needs highly vulnerable to various insults. This led to a general view that oligodendrocytes are defenseless victims during brain damage such as occurs in acute and chronic CNS inflammation. However, this view is challenged by increasing evidence that oligodendrocytes are capable of expressing a wide range of immunomodulatory molecules. They express various cytokines and chemokines (e.g. Il-1β, Il17A, CCL2, CXCL10), antigen presenting molecules (MHC class I and II) and co-stimulatory molecules (e.g. CD9, CD81), complement and complement receptor molecules (e.g. C1s, C2 and C3, C1R), complement regulatory molecules (e.g. CD46, CD55, CD59), tetraspanins (e.g. TSPAN2), neuroimmune regulatory proteins (e.g. CD200, CD47) as well as extracellular matrix proteins (e.g. VCAN) and many others. Their potential immunomodulatory properties can, at specific times and locations, influence ongoing immune processes as shown by numerous publications. Therefore, oligodendrocytes are well capable of immunomodulation, especially during the initiation or resolution of immune processes in which subtle signaling might tip the scale. A better understanding of the immunomodulatory oligodendrocyte can help to invent new, innovative therapeutic interventions in various diseases such as Multiple Sclerosis. This article is part of a Special Issue entitled SI: Myelin Evolution.

Astrocyte roles in traumatic brain injury

Astrocytes sense changes in neural activity and extracellular space composition. In response, they exert homeostatic mechanisms critical for maintaining neural circuit function, such as buffering neurotransmitters, modulating extracellular osmolarity and calibrating neurovascular coupling. In addition to upholding normal brain activities, astrocytes respond to diverse forms of brain injury with heterogeneous and progressive changes of gene expression, morphology, proliferative capacity and function that are collectively referred to as reactive astrogliosis. Traumatic brain injury (TBI) sets in motion complex events in which noxious mechanical forces cause tissue damage and disrupt central nervous system (CNS) homeostasis, which in turn trigger diverse multi-cellular responses that evolve over time and can lead either to neural repair or secondary cellular injury. In response to TBI, astrocytes in different cellular microenvironments tune their reactivity to varying degrees of axonal injury, vascular disruption, ischemia and inflammation. Here we review different forms of TBI-induced astrocyte reactivity and the functional consequences of these responses for TBI pathobiology. Evidence regarding astrocyte contribution to post-traumatic tissue repair and synaptic remodeling is examined, and the potential for targeting specific aspects of astrogliosis to ameliorate TBI sequelae is considered.

Innate immune response is differentially dysregulated between bipolar disease and schizophrenia

Schizophrenia (SZ) and bipolar disorder (BD) are severe psychiatric conditions with a neurodevelopmental component. Genetic findings indicate the existence of an overlap in genetic susceptibility across the disorders. Also, image studies provide evidence for a shared neurobiological basis, contributing to a dimensional diagnostic approach. This study aimed to identify the molecular mechanisms that differentiate SZ and BD patients from health controls but also that distinguish both from health individuals. Comparison of gene expression profiling in post-mortem brains of both disorders and health controls (30 cases), followed by a further comparison between 29 BD and 29 SZ revealed 28 differentially expressed genes. These genes were used in co-expression analysesthat revealed the pairs CCR1/SERPINA1, CCR5/HCST, C1QA/CD68, CCR5/S100A11 and SERPINA1/TLR1 as presenting the most significant difference in co-expression between SZ and BD. Next, a protein-protein interaction (PPI) network using the 28 differentially expressed genes as seeds revealed CASP4, TYROBP, CCR1, SERPINA1, CCR5 and C1QA as having a central role in the diseases manifestation. Both co-expression and network topological analyses pointed to genes related to microglia functions. Based on this data, we suggest that differences between SZ and BP are due to genes involved with response to stimulus, defense response, immune system process and response to stress biological processes, all having a role in the communication of environmental factors to the cells and associated to microglia.

Immunological barriers to stem cell therapy in the central nervous system

The central nervous system is vulnerable to many neurodegenerative disorders such as Alzheimer's disease that result in the extensive loss of neuronal cells. Stem cells have the ability to differentiate into many types of cells, which make them ideal for treating such disorders. Although stem cell therapy has shown some promising results in animal models for many brain disorders it has yet to translate into the clinic. A major hurdle to the translation of stem cell therapy into the clinic is the immune response faced by stem cell transplants. Here, we focus on immunological and related hurdles to stem cell therapies for central nervous system disorders.

Flaviviruses are neurotropic, but how do they invade the CNS?

Flaviruses (FV) are RNA viruses carried by mosquitoes. Neurological signs including acute encephalitis, meningitis and acute flaccid paralysis develop in a small percentage of infected individuals; long term sequlae are, Parkinsonism, dystonias and cognitive changes. FV neuroinfection is neurotropic involving subcortical nuclei (substantia nigra and thalamus) anterior horn neurons and neocortex. Glycosylation of the FV E envelope protein is one determinant of neuroinvasion, increasing both axonal and trans-epithelial transportation. Neutralizing antibodies against the E and NS proteins prevents FV uptake into several cell types, including axons. CD8+ T cells are vital for clearance of WNF infected cells from the CNS, whereas TLR-3 and TLR-7 mediated anti-virus response through increased serum inflammatory cytokines to disrupt the BBB providing infected leucocytes and free virus access to the CNS (so called Trojan horse) Cellular virus attachment factors, promoting FV cell entry are widely distributed and include DC-SIGN (that detects complex carbohydrate molecules); Glycosamino glycans (GAG), Heparan sulphate(HSPG) Semaphorin 7A, Low Density Lipid receptors (LDLR); these are not FV specific virus entry receptors. The FV also crosses epithelial and endothelial barriers by disrupting Tight Junction complexes to increase BBB permeability. This review describes the multiple pathways responsible for the neuroinvasive properties of the Flaviviruses.

Differential expression of transcription factors and inflammation-, ROS-, and cell death-related genes in organotypic cultures in the modiolus, the organ of Corti and the stria vascularis of newborn rats

Cells respond to injury and hypoxia by changing gene expression. To study how the main compartments of the cochlea, the stria vascularis (SV), the organ of Corti (OC), and the modiolus (MOD), respond to such stress, we analyzed the expression of selected genes using microarray analysis. Organotypic cultures of SV, OC, and MOD from newborn rats were used as an experimental model. In the present study, we compare the expression of a total of 50 genes involved in apoptosis and necrosis, reactive oxygen species (ROS) metabolism, inflammation as well as selected transcription factors (TF) and analyze their role for the different cell death patterns observed in the three regions. MOD, OC, and SV differ not only in their basal gene profiles but also in their ability to respond to injury and hypoxia. The results provide two coexpression clusters across the three regions, a Hif-1a coexpression cluster and a cluster around the cell death-associated transcripts Casp3, Capn1, Capn2, and Capns1. These clusters include the TF Jun, Bmyc, Nfyc, Foxd3, Hes1, the ROS-associated molecules Sod3, and Nos2, and the inflammatory chemokine Ccl20. The evidence of both clusters indicates the complex and regulated character of gene expression following injury and hypoxia across the three regions SV, OC, and MOD. The high vulnerability of spiral ganglion neurons in the MOD region, previously explained on the basis of the availability of neuro-trophic factors, is associated with the increased endogenous production of ROS and nitric oxide and inadequate activation of protective acting genes.

Reactive gliosis and the multicellular response to CNS damage and disease

The CNS is prone to heterogeneous insults of diverse etiologies that elicit multifaceted responses. Acute and focal injuries trigger wound repair with tissue replacement. Diffuse and chronic diseases provoke gradually escalating tissue changes. The responses to CNS insults involve complex interactions among cells of numerous lineages and functions, including CNS intrinsic neural cells, CNS intrinsic nonneural cells, and CNS extrinsic cells that enter from the circulation. The contributions of diverse nonneuronal cell types to outcome after acute injury, or to the progression of chronic disease, are of increasing interest as the push toward understanding and ameliorating CNS afflictions accelerates. In some cases, considerable information is available, in others, comparatively little, as examined and reviewed here.

Toll-like 4 receptor inhibitor TAK-242 decreases neuroinflammation in rat brain frontal cortex after stress

Background

The innate immune response is the first line of defence against invading microorganisms and it is also activated in different neurologic/neurodegenerative pathological scenarios. As a result, the family of the innate immune toll-like receptors (TLRs) and, in particular, the genetic/pharmacological manipulation of the TLR-4 signalling pathway emerges as a potential therapeutic strategy. Growing evidence relates stress exposure with altered immune responses, but the precise role of TLR-4 remains partly unknown.

Methods

The present study aimed to elucidate whether the elements of the TLR-4 signalling pathway are activated after acute stress exposure in rat brain frontal cortex and its role in the regulation of the stress-induced neuroinflammatory response, by means of its pharmacological modulation with the intravenous administration of the TLR-4 specific inhibitor TAK-242. Considering that TLR-4 responds predominantly to lipopolysaccharide from gram-negative bacteria, we checked whether increased intestinal permeability and a resultant bacterial translocation is a potential regulatory mechanism of stress-induced TLR-4 activation.

Results

Acute restraint stress exposure upregulates TLR-4 expression both at the mRNA and protein level. Stress-induced TLR-4 upregulation is prevented by the protocol of antibiotic intestinal decontamination made to reduce indigenous gastrointestinal microflora, suggesting a role for bacterial translocation on TLR-4 signalling pathway activation. TAK-242 pre-stress administration prevents the accumulation of potentially deleterious inflammatory and oxidative/nitrosative mediators in the brain frontal cortex of rats.

Conclusions

The use of TAK-242 or other TLR-4 signalling pathway inhibitory compounds could be considered as a potential therapeutic adjuvant strategy to constrain the inflammatory process taking place after stress exposure and in stress-related neuropsychiatric diseases.

Novel frontiers in epilepsy treatments: preventing epileptogenesis by targeting inflammation

Currently available epilepsy drugs only affect the symptoms (seizures), and there is a need for innovative treatments that target the underlying disease. Increasing evidence points to inflammation as a potentially important mechanism in epileptogenesis. In the last decade, a new generation of etiologically realistic syndrome-specific experimental models have been developed, which are expected to capture the epileptogenic mechanisms operating in corresponding patient populations, and to exhibit similar treatment responsiveness. Recently, an intervention known to have broad-ranging anti-inflammatory effects (selective brain cooling) has been found to prevent the development of spontaneously occurring seizures in an etiologically realistic rat model of post-traumatic epilepsy. Several drugs used clinically for other indications also have the potential for inhibiting inflammation, and should be investigated for antiepileptogenic activity in these models. If results of such studies are positive, these compounds could rapidly enter Phase III trials in patients at high risk of developing epilepsy.

Interplay between human microglia and neural stem/progenitor cells in an allogeneic co-culture model

Experimental neural cell therapies, including donor neural stem/progenitor cells (NPCs) have been reported to offer beneficial effects on the recovery after an injury and to counteract inflammatory and degenerative processes in the central nervous system (CNS). The interplay between donor neural cells and the host CNS still to a large degree remains unclear, in particular in human allogeneic conditions. Here, we focused our studies on the interaction of human NPCs and microglia utilizing a co-culture model. In co-cultures, both NPCs and microglia showed increased survival and proliferation compared with mono-cultures. In the presence of microglia, a larger subpopulation of NPCs expressed the progenitor cell marker nestin, whereas a smaller group of NPCs expressed the neural markers polysialylated neural cell adhesion molecule, A2B5 and glial fibrillary acidic protein compared with NPC mono-cultures. Microglia thus hindered differentiation of NPCs. The presence of human NPCs increased microglial phagocytosis of latex beads. Furthermore, we observed that the expression of CD200 molecules on NPCs and the CD200 receptor protein on microglia was enhanced in co-cultures, whereas the release of transforming growth factor-β was increased suggesting anti-inflammatory features of the co-cultures. To conclude, the interplay between human allogeneic NPCs and microglia, significantly affected their respective proliferation and phenotype. Neural cell therapy including human donor NPCs may in addition to offering cell replacement, modulate host microglial phenotypes and functions to benefit neuroprotection and repair.

Different TLR4 expression and microglia/macrophage activation induced by hemorrhage in the rat spinal cord after compressive injury

Background

Hemorrhage is a direct consequence of traumatic injury to the central nervous system and may cause innate immune reactions including cerebral Toll-like receptor (TLR) 4 upregulation which usually leads to poor outcome in the traumatic brain injury. In spinal cord injury (SCI), however, how hemorrhage induces innate immune reaction in spinal parenchyma remains unknown. The present study aimed to see whether blood component and/or other factor(s) induce TLR4 and microglia/macrophages involved innate immune reactions in the rat spinal cord after traumatic injury.

Methods

Using the compressive SCI model of the rat, hemorrhage in the spinal cord was identified by hematoxylin-eosin staining. Microglia/macrophage activation, TLR4 expression, and cell apoptosis were investigated by immunohistochemistry. Nuclear factor (NF)-κB p50 level of the two segments of the cord was detected by western blotting assay. With carbon powder injection, blood origination of the hematoma was explored. The blood-spinal cord barrier (BSCB) states of the lesion site and the hematoma were compared with immunohistochemistry and tannic acid-ferric chloride staining.

Results

Histological observation found blood accumulated in the center of compression lesion site (epicenter) and in the hematoma approximately 1.5 cm away from the epicenter. TLR4 expression, microglia//macrophage activation, and subsequent apoptosis in the area of far-away hematoma were late and weak in comparison to that in epicenter. In addition, TLR4 positive microglia/macrophages appeared to be phagocytotic in the far-away hematoma more obviously than that in the epicenter. Injected carbon powder indicated that accumulated blood of the far-away hematoma originated from the bleeding of the lesion epicenter, and the BSCB around the hematoma was not compromised in the early phase. Accordingly, at 3 days post injury, NF-κB p50 was upregulated based on the similar levels of blood component hemoglobin, and cell apoptosis was obvious in the epicenter but not in the far-away hematoma.

Conclusion

These data suggest that besides blood component, BSCB compromise and the extent of tissue injury contribute more to TLR4 and microglia/macrophage responses to the spinal cord hemorrhage. Therefore, the innate immune environment is a necessary consideration for the SCI therapy targeting TLR4 and microglia/macrophages.

SARM is required for neuronal injury and cytokine production in response to central nervous system viral infection

Four of the five members of the Toll/IL-1R domain-containing adaptor family are required for signaling downstream of TLRs, promoting innate immune responses against different pathogens. However, the role of the fifth member of this family, sterile α and Toll/IL-1R domain-containing 1 (SARM), is unclear. SARM is expressed primarily in the CNS where it is required for axonal death. Studies in Caenorhabditis elegans have also shown a role for SARM in innate immunity. To clarify the role of mammalian SARM in innate immunity, we infected SARM(-/-) mice with a number of bacterial and viral pathogens. SARM(-/-) mice show normal responses to Listeria monocytogenes, Mycobacterium tuberculosis, and influenza virus, but show dramatic protection from death after CNS infection with vesicular stomatitis virus. Protection correlates with reduced CNS injury and cytokine production by nonhematopoietic cells, suggesting that SARM is a positive regulator of cytokine production. Neurons and microglia are the predominant source of cytokines in vivo, supporting a role for SARM as a link between neuronal injury and innate immunity.

Stress-induced neuroinflammation: role of the Toll-like receptor-4 pathway

BACKGROUND

Stressful challenges are associated with variations in immune parameters, including increased innate immunity/inflammation. Among possible mechanisms through which brain monitors peripheral immune responses, toll-like receptors (TLRs) recently emerged as the first line of defense against invading microorganisms. Their expression is modulated in response to pathogens and other environmental stresses.

METHODS

Taking into account this background, the present study aimed to elucidate whether the toll-like receptor-4 (TLR-4) signaling pathway is activated after repeated restraint/acoustic stress exposure in mice prefrontal cortex (PFC), the potential regulatory mechanism implicated (i.e., bacterial translocation), and its role in conditions of stress-induced neuroinflammation, using a genetic strategy: C3H/HeJ mice with a defective response to lipopolysaccharide stimulation of TLR-4.

RESULTS

Stress exposure upregulates TLR-4 pathway in mice PFC. Stress-induced inflammatory nuclear factor κB activation, upregulation of the proinflammatory enzymes nitric oxide synthase and cyclooxygenase type 2, and cellular oxidative/nitrosative damage are reduced when the TLR-4 pathway is defective. Conversely, TLR-4 deficient mice presented higher levels of the anti-inflammatory nuclear factor peroxisome proliferator activated receptor-gamma after stress exposure than control mice. The series of experiments using antibiotic intestinal decontamination also suggest a role for bacterial translocation on TLR-4 activation in PFC after stress exposure.

CONCLUSIONS

Taken together, all the data presented here suggest a bifunctional role of TLR-4 signaling pathway after stress exposure by triggering neuroinflammation at PFC level and regulating gut barrier function/permeability. Furthermore, our data suggest a possible protective role of antibiotic decontamination in stress-related pathologies presenting increased intestinal permeability (leaky gut) such as depression, showing a potential therapeutic target that deserves further consideration.

Controlled cortical impact and craniotomy induce strikingly similar profiles of inflammatory gene expression, but with distinct kinetics

An immediate consequence of traumatic brain injury (TBI) is the induction of an inflammatory response. Mounting data suggest that inflammation is a major contributor to TBI-induced brain damage. However, much remains unknown regarding the induction and regulation of the inflammatory response to TBI. In this study we compared the TBI-induced inflammatory response to severe parenchymal injury (controlled cortical impact) vs. mild brain injury (craniotomy) over a 21-day period. Our data show that both severe and mild brain injury induce a qualitatively similar inflammatory response, involving highly overlapping sets of effector molecules. However, kinetic analysis revealed that the inflammatory response to mild brain injury is of much shorter duration than the response to severe TBI. Specifically, the inflammatory response to severe brain injury persists for at least 21 days, whereas the response to mild brain injury returns to near baseline values within 10 days post-injury. Our data therefore imply that the development of accurate diagnostic tests of TBI severity that are based on imaging or biomarker analysis of the inflammatory response may require repeated measures over at least a 10-day period, post-injury.

Short and long-term analysis and comparison of neurodegeneration and inflammatory cell response in the ipsilateral and contralateral hemisphere of the neonatal mouse brain after hypoxia/ischemia

Understanding the evolution of neonatal hypoxic/ischemic is essential for novel neuroprotective approaches. We describe the neuropathology and glial/inflammatory response, from 3 hours to 100 days, after carotid occlusion and hypoxia (8% O₂, 55 minutes) to the C57/BL6 P7 mouse. Massive tissue injury and atrophy in the ipsilateral (IL) hippocampus, corpus callosum, and caudate-putamen are consistently shown. Astrogliosis peaks at 14 days, but glial scar is still evident at day 100. Microgliosis peaks at 3–7 days and decreases by day 14. Both glial responses start at 3 hours in the corpus callosum and hippocampal fissure, to progressively cover the degenerating CA field. Neutrophils increase in the ventricles and hippocampal vasculature, showing also parenchymal extravasation at 7 days. Remarkably, delayed milder atrophy is also seen in the contralateral (CL) hippocampus and corpus callosum, areas showing astrogliosis and microgliosis during the first 72 hours. This detailed and long-term cellular response characterization of the ipsilateral and contralateral hemisphere after H/I may help in the design of better therapeutic strategies.

Challenging the role of adaptive immunity in neurotrauma: Rag1(-/-) mice lacking mature B and T cells do not show neuroprotection after closed head injury

The role of adaptive immunity in contributing to post-traumatic neuroinflammation and neuropathology after head injury remains largely unexplored. The present study was designed to investigate the pathophysiological sequelae of closed head injury in Rag1(-/-) mice devoid of mature B and T lymphocytes. C57BL/6 wild-type and Rag1(-/-) mice were subjected to experimental closed head injury, using a standardized weight-drop device. Outcome parameters consisted of neurological scoring, quantification of blood-brain barrier (BBB) function, measurement of inflammatory markers and mediators of apoptosis in serum and brain tissue, and assessment of neuronal cell death, astrogliosis, and tissue destruction. There was no difference between wild-type and Rag1(-/-) mice with regard to injury severity and neurological impairment for up to 7 days after head injury. The extent of BBB dysfunction was in a similar range for both groups. Quantification of complement activation fragments in serum revealed significantly attenuated C3a levels in Rag1(-/-) mice compared to wild-type animals. In contrast, the levels of pro- and anti-inflammatory cytokines and pro-apoptotic and anti-apoptotic mediators remained in a similar range for both groups, and the histological analysis of brain sections did not reveal a difference in reactive astrogliosis, tissue destruction, and neuronal cell death in Rag1(-/-) compared to wild-type mice. These findings suggest that adaptive immunity is not of crucial importance for initiating and sustaining the inflammatory neuropathology after closed head injury. The attenuated extent of post-traumatic complement activation seen in Rag1(-/-) mice implies a cross-talk between innate and adaptive immune responses, which requires further investigation in future studies.

Inflammation in Parkinson's disease

Parkinson's disease (PD) is a common neurodegenerative disease that is characterized by the degeneration of dopaminergic neurons in the substantia nigra pars compacta. Inflammatory responses manifested by glial reactions, T cell infiltration, and increased expression of inflammatory cytokines, as well as other toxic mediators derived from activated glial cells, are currently recognized as prominent features of PD. The consistent findings obtained by various animal models of PD suggest that neuroinflammation is an important contributor to the pathogenesis of the disease and may further propel the progressive loss of nigral dopaminergic neurons. Furthermore, although it may not be the primary cause of PD, additional epidemiological, genetic, pharmacological, and imaging evidence support the proposal that inflammatory processes in this specific brain region are crucial for disease progression. Recent in vitro studies, however, have suggested that activation of microglia and subsequently astrocytes via mediators released by injured dopaminergic neurons is involved. However, additional in vivo experiments are needed for a deeper understanding of the mechanisms involved in PD pathogenesis. Further insight on the mechanisms of inflammation in PD will help to further develop alternative therapeutic strategies that will specifically and temporally target inflammatory processes without abrogating the potential benefits derived by neuroinflammation, such as tissue restoration.

Astrocyte and macrophage regulation of YKL-40 expression and cellular response in neuroinflammation

Numerous inflammatory conditions are associated with elevated YKL-40 expression by infiltrating macrophages. Thus, we were surprised to observe minimal macrophage and abundant astrocyte expression of YKL-40 in neuroinflammatory conditions. The aims of the current study were to better delineate this discrepancy, characterize the factors that regulate YKL-40 expression in macrophages and astrocytes and study whether YKL-40 expression correlates with cell morphology and/or activation state. In vitro, macrophages expressed high levels of YKL-40 that was induced by classical activation and inhibited by alternative activation. Cytokines released from macrophages induced YKL-40 transcription in astrocytes that was accompanied by morphological changes and altered astrocytic motility. Because coculturing of astrocytes and macrophages did not reverse this in vitro expression pattern, additional components of the in vivo central nervous system (CNS) milieu must be required to suppress macrophage and induce astrocyte expression of YKL-40.

Molecular mechanisms of inflammation and tissue injury after major trauma--is complement the "bad guy"?

Trauma represents the leading cause of death among young people in industrialized countries. Recent clinical and experimental studies have brought increasing evidence for activation of the innate immune system in contributing to the pathogenesis of trauma-induced sequelae and adverse outcome. As the "first line of defense", the complement system represents a potent effector arm of innate immunity, and has been implicated in mediating the early posttraumatic inflammatory response. Despite its generic beneficial functions, including pathogen elimination and immediate response to danger signals, complement activation may exert detrimental effects after trauma, in terms of mounting an "innocent bystander" attack on host tissue. Posttraumatic ischemia/reperfusion injuries represent the classic entity of complement-mediated tissue damage, adding to the "antigenic load" by exacerbation of local and systemic inflammation and release of toxic mediators. These pathophysiological sequelae have been shown to sustain the systemic inflammatory response syndrome after major trauma, and can ultimately contribute to remote organ injury and death. Numerous experimental models have been designed in recent years with the aim of mimicking the inflammatory reaction after trauma and to allow the testing of new pharmacological approaches, including the emergent concept of site-targeted complement inhibition. The present review provides an overview on the current understanding of the cellular and molecular mechanisms of complement activation after major trauma, with an emphasis of emerging therapeutic concepts which may provide the rationale for a "bench-to-bedside" approach in the design of future pharmacological strategies.

Overexpression of the immunoreceptor CD300f has a neuroprotective role in a model of acute brain injury

It is well known that cell surface immune receptors play a critical role in regulating immune and inflammatory processes in the central nervous system (CNS). We have analyzed the function of cluster of differentiation (CD)300f immunoreceptor in a model of excitotoxic rat brain damage. First, to explore the presence of endogenous ligand(s) for this receptor we used a human CD300f-Ig soluble protein and confocal microscopy, showing specific staining mainly in CNS white matter and on the surface of oligodendrocytes and certain astrocytes. Next, we demonstrated in a model of in vivo rat brain excitotoxic damage that the overexpression of human CD300f induced a significant reduction in the lesion volume. To validate these results, we cloned the rat ortholog of CD300f protein (rCD300f). The overexpression of rCD300f receptor had a comparable neuroprotective effect after the acute brain injury and a similar CNS staining pattern when stained with the rCD300f-Ig soluble protein. Interestingly, when we analyzed the expression pattern of rCD300f in brain cells by quantitative polymerase chain reaction and immunohistochemistry, we detected the expression of CD300f as expected in microglial cells, but also in oligodendrocytes and neurons. These data suggest that the neuroprotective role of CD300f would be the result of a complex network of cell interactions.